Two types of Solar Water Heaters are available; one based on flat plate collectors and the other based on evacuated tube collectors. Flat plate collector (FPC) based systems are of metallic type and have longer life as compared to Evacuated tube collector (ETC) based system because ETCs are made of glass which are of fragile in nature. Both these systems are available with and without heat exchanger. They can also work with and without pump. Systems without pump are known as Thermosyphon systems and those with pump are known as forced circulation systems.
The main part of the Solar Water Heating System is the Flat Plate Collector or in common ‘PANEL’. Metallic strip (mainly of Copper) is coated with thin layers of Nickel and Chromium, which is called as Solar Selective Coating. This selective coating ensures highest degree of absorption of Solar Heat and least possible emission of the same. This results in optimal utilization of the Solar Heat. There are two types of processes based on the operating methods, thermo-siphon and forced flow.